Fix voxel rendering with orthographic camera

[jjhembd]

Description

This PR corrects the calculation of the starting view ray in VoxelFS.glsl to account for orthographic cameras.

In the usual perspective camera, the view rays all originate from the camera position and emanate in a direction that depends on the screen pixel. The camera in this case is perhaps best understood as an eye, with the screen pixels corresponding to different angular directions from a focal point.

In an orthographic camera, all view rays are exactly parallel, with the different pixels corresponding to different ray origins.

Along with the new logic in VoxelFS, code changes include:

• New uniform cameraDirectionUv in VoxelPrimitive.
• Removed the (unused, undocumented) viewDirWorld property from the fsInput.voxel struct, to facilitate pulling the ray calculation out into a helper function.

Issue number and link

Resolves #11013

Testing plan

Load the "Voxels" Sandcastle, and use the projection picker to switch between perspective and orthographic cameras. The voxel should render correctly in both projections, with the globe partially visible through the semi-transparent voxels. The orthographic effect may be most obvious with the "Box" examples.

Author checklist

• I have submitted a Contributor License Agreement
• I have added my name to CONTRIBUTORS.md
• I have updated CHANGES.md with a short summary of my change
• I have added or updated unit tests to ensure consistent code coverage
• I have updated the inline documentation, and included code examples where relevant
• I have performed a self-review of my code

[github-actions]

Thank you for the pull request, @jjhembd!

✅ We can confirm we have a CLA on file for you.

[ggetz]

Thanks @jjhembd! This PR is in a great state. Code here is looking great and the functionality is working exactly as expected. I also doubled checked the voxel picking example in orthographic as well.

Is it possible to add any kind of unit test to verify?

[ggetz]

@jjhembd I'm seeing the following error when I run the e2e example:

That seems to happen for any voxel example, even before this PR. I'm unable to duplicate in Sandcastle. I'm thinking it may have to do with chrome headless.

[jjhembd]

@ggetz, on my machine, this line in playwright.config.js was the issue:

        launchOptions: {
          // this forces chrome to use the gpu for webgl which greatly speeds up tests
          args: ["--use-angle=gl"],
        },

If I change the args to

          args: ["--use-angle=vulkan"],

the screenshots are generated normally.

I got the tip from microsoft/playwright#11627. The same thread said that --use-gl=egl worked on a Mac.

I didn't immediately see a way to setup fallbacks, so the same playwright.config.js could work on all platforms. Maybe @jjspace understands this config better?

[ggetz]

Thanks @jjhembd. If everything is working on your machine with e2e, let's move forward. Everything is looking good otherwise, and I was having the same issue here as I was in main.

FWIW, the other tests are all working for me without tweaking the playwright config. It's specifically the voxel examples, including the existing sandcastles, which aren't compiling the shader correctly in headless when running test-e2e.